The present invention relates to portable battery-powered computers.
The Ongoing Downsizing of Portable Personal Computers
Portable personal computers were introduced in the early 1980s, and proved to be very useful and popular. As this market has developed, it has become increasingly clear that users strongly desire systems to have small volume, small weight, and long battery-powered lifetime. Thus, small portable computers ("laptop" computers) have proven extremely popular during the late 1980s. Users continue to demand more features, longer time between recharges, and lower weight and volume. This combination of demands is difficult to meet. Moreover, as of 1990, another smaller generation of portable computers has begun to appear, referred to as "notebook" computers. This smaller form factor will only exacerbate the difficulty of the above tradeoffs.
Approaches to Power Conservation
There are three basic approaches to extending the operating lifetime of a portable computer. The simplest way is to specify components at the lowest economical power consumption. Thus, for instance, CMOS integrated circuits and liquid crystal displays (LCDs) will normally be used. An equally simple way is to increase battery capacity. However, both of these routes rapidly encounter limits, which are set simply by the tradeoff of the cost of lower-power components, or of the elimination of functionality, with user expectations.
The third way is to use power-management algorithms so that, at almost every instant, all components are being operated in the lowest-power mode for their current demands. Thus, for example, a processor which is not currently executing a program may be placed into "sleep" mode, to reduce its overall power consumption. For another example, substantial power savings can be achieved simply by stopping the system clock (or by slowing down the system clock to a very low rate). For another example, it is common practice, in portable computers with an LCD display, to provide backlighting for use of the display under low-light conditions; but. since this backlighting consumes relatively large amounts of power, it will normally be turned off after a short period of inactivity (or even, alternatively, after a short duration regardless of activity), until the user again demands backlighting.
All of these lines of approach have some inherent limits. For example, it is hard to foresee any integrated circuit technology which would be economical in the 1990s and more power-efficient than low-power low-voltage CMOS. Some further improvement in this area is foreseeable, but no revolutionary improvements appear likely. Moreover, in practice, such improvements are largely outside the control of system designers: when lower-power chips are sampled, system design houses will buy them; but system design houses cannot greatly accelerate the pace of introduction of such chips.
It is also true that the smartest power-management programs cannot reduce the time fraction during which the user wishes to look at the display, or enter data through the keyboard. However, in this area there does appear to be room for improvement, and system design improvements can help achieve power efficiency.
Many power management schemes have been proposed, where parts of the system are shut down during periods of inactivity.sup.1. These approaches tend to extend the usable working time between recharges. FNT .sup.1 One example of a portable computer system with power-monitoring functions is described in U.S. Pat. No. 4,980,836 to Carter et al., which is hereby incorporated by reference. Another source of proposed teachings regarding power-management functions is provided by the DS1227 product preview, contained in the 1988 data book of Dallas Semiconductor Corporation, which is hereby incorporated by reference.
In addition, it has been recognized that management of the charging and discharging cycles of Ni-Cd batteries can help to extend their life.
Either of these power-management functions requires some intelligent control. The conventional way to implement this has been using the main microprocessor (CPU). To accomplish this, the necessary program steps are inserted into the BIOS software (basic input/output system software), which is stored in ROM.
The Use of Standby Modes
Laptop computer systems will typically have an automatic power-down function. Since some of the components use significant power, even when no computation or input is occurring, the system will send itself into a standby or sleep mode if the user has not provided any input for a given period of time (e.g. 30 seconds or five minutes). (Sleep mode may not normally be entered, however, if new information is still being written to the display.)
There are various enhancements which have been proposed to the scheme. For example, it may be desirable to blank the display after a certain length of inactivity and shut down the system clock only after an additional length of inactivity.
Thus, there may be more than one reduced-power mode. For example, in the presently preferred embodiment a "standby" mode is used to transiently power-down subsystems (such as the display or the hard disk) without stopping the CPU. For deeper inactivity, a "sleep" mode can also be entered, in which nearly all functions of the system are turned off. From the standpoint of power consumption, entering sleep mode is almost the same as turning a conventional nonportable machine off (except that data will not be lost).
Commanding Entry into a Reduced-Power Mode
Most Laptop or Notebook computers that feature a Standby, Sleep, or Resume mode (e.g. Compaq's SLT and LTE families, most of the Toshiba portable family, and the Dell 316 and 320LT) have a Standby Button which, when pushed, puts the computer into Standby Mode. In the standard implementation, there is a separate Sleep Button and "case-closed" sensor (although on some of the less expensive or smallest units, the case-closed sensor may be left off completely), and the Sleep Button only recognizes one mode of push, regardless of the push duration.
By using two button/microswitch devices, more PCB real estate is required, more cost is added, and reliability is not as good, because one device depends on the other for proper activation of the Standby Mode. In this way, if either device fails, the Standby Mode will not be activated during case closure.
For example, the Dell 316 and 320 LT Laptop computers (which have a larger available volume than the "notebook" computer of the presently preferred embodiment) include a "case-closed" microswitch, separate from the button used to control entry into standby mode. This microswitch (located under the latch flap), was tripped whenever the screen was lowered and latched into position. The following events would then happen:
a) The screen's backlight was turned off.
b) A beeper was sounded to alert the user of "case-closed while ON" condition.
c) A power saving mode was entered, slowing down the processor, and turning off all unnecessary features.
In addition to this case-closing microswitch, a separate Standby Button was located adjacent to the keyboard area. This Standby Button was only accessible when the computer screen was opened. When this button was depressed (regardless of the duration) a Standby Mode would be entered until the button was depressed a second time, "waking up" the computer from Standby (also called Sleep) Mode.
In very small "notebook"-size computers, the amount of available circuit board space is very small. Each physical switch consumes board space for its connector. Moreover, each switch or button will itself require a nonzero volume, and this volume may become significant in relation to a very small total system volume.
Portable Computer with Dual-Purpose Standby Switch
The present invention provides a mechanism for efficiently controlling transitions into or out of either of two reduced-power states, using a single pushbutton. The button is positioned to be depressed either by closing the case, or by a push from the user's finger. The significance of a button signal is detected by monitoring HOW the button is pushed: a simple time computation determines whether the button's depression is momentary or extended. The appropriate mode transition can then be made.
This configuration provides an input to control activation or deactivation of a "Standby" mode during normal computer usage, while also detecting a "case-closed" condition. This modified button device replaces two separate devices--one button, and one microswitch--in more standard portable implementations.
The disclosed innovations provide a notebook computer in which the case-closed microswitch, and the Standby button, are replaced by a single button. This single button can be pressed by the user whenever the case is open. This button is positioned so that it will be held down whenever the case's cover is closed.
In the presently preferred embodiment, the combined button has a cam-like surface, for better mechanical interface with the case cover.
A software procedure polls the state of this combined button. By monitoring the duration during which the button stays down, the system can distinguish between a user pushing the Standby Button while the case is opened (momentary push) or a user closing the case while the computer is still on (an extended push--greater than some software-definable period of time). Thus, the software can detect the need for a transition into or out of the appropriate reduced-power state, depending on HOW the button is pushed.
A momentary push tells the software to put the unit into Standby until another momentary push is encountered, after which the computer will "wake up" to continue normal operation.
An extended push tells the software to put the system into a "sleep" mode, which provides the greatest possible power conservation (without loss of data). In this case the system remains in sleep mode until the Button is released, at which point the system would "wake up" to continue normal operation.
Of course, the system may have only the "sleep" or only the "standby" mode. In that case, the momentary push (off) has the same effect as closing the case of cause the system to go into the "sleep" or "standby" mode.
In the presently preferred embodiment, the duration threshold for distinguishing a momentary push from an extended push is preferably software-programmable.
Some significant advantages of the present invention include:
a) Saves space by combining two devices into one.
b) Saves cost by eliminating one microswitch per unit.
c) Improves reliability by combining two interdependent devices into one.
This disclosed invention is especially advantageous in Notebook-size computers, since they inherently have the on-board "intelligence" to distinguish HOW the button was pushed, and because full-function computing devices are getting smaller, more cost-sensitive, and greater reliability is demanded--and this device helps to satisfy all of these conditions.